The present invention relates to polycrystalline diamond (PCD) or cubic boron nitride (CBN) compacts made by a high pressure/high temperature process (HP/HT) and more particularly to such compact in supported configuration having substantially flat support interfaces.
A compact is a sintered polycrystalline mass of abrasive particles (e.g. diamond) bonded together to form an integral, tough, coherent, high strength mass. A composite compact is a compact bonded to a substrate material, such as a cemented metal carbide (e.g. cobalt cemented tungsten carbide). The metal bonded carbide mass generally is selected from the group consisting of tungsten, titanium, tantalum carbides and mixtures thereof with metal bonding material therein normally being present in a quantity from about 6 to 25 weight percent and selected from the group consisting of cobalt, nickel, iron and mixtures thereof. Other metal carbides can be used.
Compacts or composite compacts may be used as blanks for cutting tools, drill bits, dressing tools, and wear parts. Compacts made in a cylindrical configuration have been used to make wire drawing dies (see U.S. Pat. No. 3,381,428).
One method for manufacturing diamond compacts involves the steps of:
A. placing within a protective shield metal enclosure which is disposed within the reaction cell of an HP/HT apparatus; PA0 B. subjecting the contents of the cell to conditions of temperature, pressure and time (typically at least 50 kbar, at least 1300.degree. C. and 3-120 minutes) sufficient to give bonding between adjacent crystal grains.
(1) a mass of diamond crystals; PA1 (2) a mass of catalyst metal or alloy containing catalyst metal in contact with the mass of diamond crystals; and PA1 (3) optionally, a mass of metal cemented carbide; and
The mass of catalyst metal could be in the form of a disc of one of the well known catalyst or an alloy containing at least one catalyst metal for diamond crystallization. Under the HP/HT condition, a wave of liquid metal advances through the dense diamond (or CBN material as described below), and the catalyst metal (in liquid form) makes itself available as a catalyst or solvent for recrystallization or crystal intergrowth. The terms catalyst and catalyst/solvent are used interchangeably. This process is sometimes known as the sweep-through method, i.e. the catalyst sweeps (or advances or diffuses) through the crystalline mass.
The relative shapes of the abrasive mass and catalyst can be varied. For example, the mass of diamond can be cylindrical, and the catalyst can be an annular shape surrounding the cylinder of abrasive crystals or a disc on top or below the diamond mass.
The source of catalyst may also be cemented metal carbide or carbide molding powder (which may be cold pressed to shape) wherein the cementing agent is a catalyst or solvent for diamond recrystallization or growth.
The catalyst is generally selected from cobalt, nickel and iron, but can be selected from any of the known catalysts which also include ruthenium, rhodium, palladium, platinum, chromium, manganese, tantalum or mixtures or alloys of catalysts. Catalyst may be mixed with the abrasive crystals in addition to or instead of being a separate mass adjacent to the abrasive crystals.
High temperature and high pressure in the diamond stable region are applied for a time sufficient to bond or sinter the diamond crystals together. The diamond stable region is the range of pressure temperature conditions under which diamond is thermodynamically stable. On a pressure-temperature phase diagram, it is the high pressure side, above the equilibrium line between diamond and graphite. The resulting compact is characterized particularly by diamond-to-diamond bonding, i.e., bonding between adjacent grains whereby there are parts of the crystal lattice which are shared between neighboring crystal grains (resulting from recrystallization at HP/HT conditions). The diamond concentration preferably is at least 70 volume percent of the diamond mass (i.e. excluding any substrate mass). Methods for making diamond compacts are detailed in U.S. Pat. Nos. 3,141,746; 3,745,623; 3,609,818; 3,831,428; and 3,850,591 (all of which are incorporated herein by reference).
Cubic boron nitride compacts are manufactured in a similar manner to that just described for diamond. However, in making a CBN compact by the sweep-through method, the metal swept through into the CBN crystal mass may or may not be a catalyst or solvent for CBN recrystallization. Thus, a mass of polycrystalline CBN can be bonded to a cobalt cemented tungsten carbide substrate by sweep through of the cobalt ingredient into the interstices of the CBN mass under HP/HT conditions, even though cobalt is not a catalyst for CBN. This interstitial cobalt binds the polycrystalline CBN to the cemented tungsten carbide substrate. Nevertheless, the term catalyst will be used to described the bonding or sintering metal swept into a CBN particle mass for the sake of convenience.
The HP/HT sintering process for CBN is carried out in the CBN stable region which is in the range of pressure and temperature conditions under which CBN is thermodynamically stable. CBN concentration is preferably at least 70 volume percent of the CBN mass. Methods for making CBN compacts are detailed in U.S. Pat. Nos. 3,233,988; 3,743,489; and 3,767,371, which are incorporated herein by reference. Crystal intergrowth or crystal-to-crystal bonding between neighboring CBN grains (as described for diamond compacts) is believed to be present.
Another form of a polycrystalline compact, which may or may not contain inter-crystal bonding, comprises a mass of diamond or CBN particles containing a second phase comprising a metal or alloy, a ceramic material, or mixtures thereof, which additional material or phase functions as a bonding agent for the abrasive particles. Polycrystalline diamond and polycrystalline CBN compacts containing a cemented carbide material is an example of such a conjoint polycrystalline abrasive mass or compact.
Fine diamond feed material has always been more difficult to sinter by the sweep-through method. Generally, sintering becomes increasingly difficult as the feed material particle size decreases. Smaller sizes of diamond feed materials (particles having a nominal largest dimension of 4-8 microns or less) have been a problem for some time because of their large surface area and small size causes more difficulties when cleaning, handling or loading the fine powder into a reaction cell. However, it is also known that as the grain size of diamond compacts decreases, transverse rupture strength increases, thus giving compacts made with smaller particles an advantage. Another advantage is the compact's finer cutting edge which may result in less workpiece damage. Under the high pressures (e.g. 50 kbar and greater) applied during the HP/HT process, such fine abrasive crystals compact resulting in a rather high packing density and a very fine pore structure. The resulting diamond mass, therefore, is dense and offers resistance to the percolation or sweep of catalyst metal through the interstices.
It is common in commercial production of supported compacts to make several in the same enclosure disposed within the reaction cell of the HP/HT apparatus. After the supported compacts are recovered from the HP/HT apparatus, they typically are subjected to finishing operations which include grinding any adhering shield metal from the outer surfaces of the compacts and often additional grinding in order to produce, for example, a cylindrical compact having a diamond or CBN table thickness and/or carbide support thickness that falls within product specifications established by the manufacturer. Especially with respect to the PCD and CBN compacts, a substantially uniform abrasive layer thickness is desirable since the blanks often are cut by the manufacturer or user into a variety of configurations (e.g. pie-shaped wedges) and the abrasive table or layer should be substantially uniform on each of such final products. The supported compact blanks recovered from the HP/HT apparatus already have been exposed to high temperature followed by cooling to about room temperature. During finishing operations, the temperature of the compact also can be elevated due to the grinding operations, cutting operations (e.g. using laser or electrodischarge machining techniques). Further, the blanks or products cut therefrom often will be mounted within tools utilizing a variety of braze techniques which further subjects the blanks or products therefrom to elevated temperature. At each of these stages of heating, the carbide support will expand to a much greater extent than will the PCD or CBN abrasive layers bonded thereto. Upon cooling, residual stresses in the pre-heated compacts naturally will be relieved. Such relief often is manifested by a compact having a non-planar bonded surface between the abrasive layer and the carbide support, thus resulting in compacts of substantially non-uniform thickness, such as is illustrated at FIG. 1 or FIG. 2 (which will be described in detail below). There is a need in the art, then, for producing compact blanks and products made therefrom that have a substantially planar interface for providing finished supported compacts of substantially uniform PCD or CBN compact thickness.